/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.messaging.support;

import java.util.Map;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.lang.Nullable;
import org.springframework.messaging.MessageHeaders;
import org.springframework.util.StringUtils;

/**
 * A base {@link HeaderMapper} implementation.
 *
 * @param <T> type of the instance to and from which headers will be mapped
 * @author Stephane Nicoll
 * @since 4.1
 */
public abstract class AbstractHeaderMapper<T> implements HeaderMapper<T> {

    protected final Log logger = LogFactory.getLog(getClass());

    private String inboundPrefix = "";

    private String outboundPrefix = "";


    /**
     * Specify a prefix to be appended to the message header name for any
     * user-defined property that is being mapped into the MessageHeaders.
     * The default is an empty String (no prefix).
     */
    public void setInboundPrefix(@Nullable String inboundPrefix) {
        this.inboundPrefix = (inboundPrefix != null ? inboundPrefix : "");
    }

    /**
     * Specify a prefix to be appended to the protocol property name for any
     * user-defined message header that is being mapped into the protocol-specific
     * Message. The default is an empty String (no prefix).
     */
    public void setOutboundPrefix(@Nullable String outboundPrefix) {
        this.outboundPrefix = (outboundPrefix != null ? outboundPrefix : "");
    }


    /**
     * Generate the name to use to set the header defined by the specified
     * {@code headerName} to the protocol specific message.
     *
     * @see #setOutboundPrefix
     */
    protected String fromHeaderName(String headerName) {
        String propertyName = headerName;
        if (StringUtils.hasText(this.outboundPrefix) && !propertyName.startsWith(this.outboundPrefix)) {
            propertyName = this.outboundPrefix + headerName;
        }
        return propertyName;
    }

    /**
     * Generate the name to use to set the header defined by the specified
     * {@code propertyName} to the {@link MessageHeaders} instance.
     *
     * @see #setInboundPrefix(String)
     */
    protected String toHeaderName(String propertyName) {
        String headerName = propertyName;
        if (StringUtils.hasText(this.inboundPrefix) && !headerName.startsWith(this.inboundPrefix)) {
            headerName = this.inboundPrefix + propertyName;
        }
        return headerName;
    }

    /**
     * Return the header value, or {@code null} if it does not exist
     * or does not match the requested {@code type}.
     */
    @Nullable
    protected <V> V getHeaderIfAvailable(Map<String, Object> headers, String name, Class<V> type) {
        Object value = headers.get(name);
        if (value == null) {
            return null;
        }
        if (!type.isAssignableFrom(value.getClass())) {
            if (logger.isDebugEnabled()) {
                logger.debug("Skipping header '" + name + "': expected type [" + type + "], but got [" +
                        value.getClass() + "]");
            }
            return null;
        } else {
            return type.cast(value);
        }
    }

}
